This is how the ETH researchers’ method works in detail: The researchers separate CO2 from the air by passing the air through a liquid containing photoacids in the dark. Since this liquid is alkaline, the CO2 reacts and forms carbonates. As soon as the salts in the liquid have accumulated to a significant degree, the researchers irradiate the liquid with light. This makes it acidic, and the carbonates transform to CO2. The CO2 bubbles out of the liquid, just as it does in a bottle of cola, and can be collected in gas tanks. When there is hardly any CO2 left in the liquid, the researchers switch off the light and the cycle starts all over again, with the liquid ready to capture CO2.
It all depends on the mixture
In practice, however, there was a problem: the photoacids used are unstable in water. “In the course of our earliest experiments, we realised that the molecules would decompose after one day,” says Anna de Vries, a doctoral student in Lukatskaya’s group and lead author of the study.
So Lukatskaya, de Vries and their colleagues analysed the decay of the molecule. They solved the problem by running their reaction not in water but in a mixture of water and an organic solvent. The scientists were able to determine the optimum ratio of the two liquids by laboratory experiments and were able to explain their findings thanks to model calculations carried out by researchers from the Sorbonne University in Paris.